Do what I did - go very slow (schlepping ). And it is really OK if you need to repeat W3D1-3. C25K is just a schedule. It works well for most, but if you have to - adjust it for your physical current state.
Tomorrow I do W5 D2 and I encountered the same feeling. How do I go from day 2 to day 3??? I usually don't look ahead til I get to the track as not to freak myself out. I think and hope this is just mental. I'll know more after tomorrow. I'm 68 and this is my first time doing c25k.